Method for controlling a vehicle parking brake

Abstract

A method for controlling a vehicle parking brake configured to apply a friction means firmly against a braking member, comprising the following steps: - detecting (22) a request for application of the brake, - depending on the parking conditions of the vehicle, determining a target value for the brake-application force for keeping said vehicle immobile, - actuating the brake so as to provide a brake-application force corresponding to the target value, characterized in that the step of determining a target value for the brake-application force value comprises the following steps: - determining a first value for the brake-application force for keeping said vehicle immobile for an unlimited duration, even after the brake has been released, - verifying (23) the presence of a driver at the driving station of the vehicle, - in the event of the driver being present at their driving station, using (24), as target value for the brake-application force, a second value strictly lower than the first value for the brake-application force, - if not, using (25) the first value for the brake-application force as target value for the brake-application force.

Description

Method of controlling a vehicle parking brake

[0001] The invention relates to a method for controlling a parking brake, also called a parking brake, for a motor vehicle.

[0002] A brake generally comprises friction means and an actuating member, also called an actuator, capable of moving the friction means towards a braking member fixed to a wheel of the vehicle. The purpose of the actuator is to bring the friction means, for example linings of a drum brake or pads of a disc brake, into contact with the braking member to brake the vehicle by friction and to move them away from the braking member in order to stop braking. When the braking system is a disc brake, the braking member is formed by a disc rotating integrally with the wheel. In the case of a drum brake, the braking member is formed by a drum rotating integrally with the wheel.

[0003] The parking brake consists of a combination of friction means and an actuator that can be controlled outside the vehicle's rolling phases, to block at least some of its wheels – generally the rear wheels – using the friction means and thus keep the vehicle stationary.

[0004] For many years, the actuator was mechanical. It is now electric and consists of an electric motor with its electronic control device, which has many advantages.

[0005] First of all, the electric actuator parking brake has a smaller footprint compared to the mechanical parking brake.

[0006] In addition, the electric actuator parking brake can be used not only for parking, but also as an emergency means for dynamic braking while the vehicle is moving.

[0007] Using an electric parking brake is also simpler for the vehicle user. When a user wants to immobilize their vehicle while parked, they simply need to command the brake to be applied, a command that can be explicit, such as by pressing a button, or implicit, such as by detecting zero speed and stopping the engine. Conversely, to get the vehicle moving again, they simply need to release the electric parking brake, a command that can again be explicit, such as pressing a button, or implicit, such as accelerating and engaging the clutch.

[0008] For use as a parking brake, the electric actuator is pre-set to ensure that the vehicle is held in position under all circumstances, taking into account its weight and possibly the slope of the road on which the vehicle is located. The application takes into account in particular the drop in brake temperature following the vehicle stopping, since it is known that this drop in temperature can lead to a release of the application force.

[0009] To eliminate the risk of the clamping force becoming too weak to prevent unwanted movement of the vehicle, the brake is therefore applied with a clamping force greater than strictly necessary, to provide a safety margin such that the release over time of the initial clamping force does not cause it to fall below a minimum clamping force necessary to hold the vehicle.

[0010] A disadvantage of this preset application is that it is often excessive, especially when the vehicle is parked for only a few seconds, for example at a traffic light. The inventors have studied the impact of this excess application. They have discovered that it results in premature brake wear and significant excess energy consumption. Safety must of course be paramount, but the present invention aims to solve this problem of premature wear and excess energy consumption without degrading the safety of the parking brake function.

[0011] Additionally, using a high clamping value increases the time it takes to release the brake when the vehicle needs to move again. This long time can cause a jerk that is less comfortable for passengers and can be annoying to the driver, who might expect better vehicle responsiveness.

[0012] To this end, the invention relates to a method for controlling a vehicle parking brake configured to apply a friction means to a braking member, comprising the following steps:

[0013] - detection of a brake application request,

[0014] - depending on the vehicle parking conditions, determination of a target clamping force value to keep said vehicle stationary,

[0015] - actuation of the brake so as to provide a clamping force corresponding to the target value,

[0016] characterized in that the step of determining a target clamping force value comprises the following steps:

[0017] - determination of a first clamping force value, allowing said vehicle to be kept stationary for an unlimited period, even after releasing the brake,

[0018] - verification of the presence of a driver in the vehicle's driving position,

[0019] - if the driver is present at the driving position, use, as the target clamping force value, of a second value strictly lower than the first clamping force value,

[0020] - otherwise, use, as the target tightening force value, the first tightening force value.

[0021] Thus, it is possible to reduce the application force of a parking brake when the driver is present in the vehicle. This avoids providing too high an application force, which contributes to premature wear of the brake, particularly of the friction means. Thanks to the proposed method, it is therefore possible to increase the service life of the brake while reducing energy consumption during braking.

[0022] The step of determining a first clamping force value makes it possible to evaluate a minimum force required to keep the vehicle stationary regardless of the vehicle's parking conditions, for an unlimited duration. Advantageously, the worst possible conditions are considered so that the minimum force determined is high enough to ensure the vehicle is safely immobilized. The first clamping force value can come from charts or tables pre-recorded in a digital computer of the vehicle.

[0023] Next, the driver's presence in the driver's seat is verified. This step indicates that the vehicle does not need to be kept stationary on its own, i.e., without human supervision. Indeed, the driver's presence implies that the driver is able to intervene if necessary.

[0024] Once the driver's presence is confirmed, a second clamping force value is determined, which is used as the target value for performing the clamping. This value is strictly lower than the first value, it is chosen to avoid the use of excessive clamping force and to reduce energy consumption without compromising braking safety. It is understood that the driver in the driving position ensures braking safety because the driver can intervene if necessary, for example when the chosen target clamping value becomes insufficient.

[0025] Thanks to the reduced clamping effort and this reduced clamping force, the time required to release the brake, when the vehicle has to start moving again, is also advantageously reduced.

[0026] Furthermore, in the case where the driver is not present at the driving position, the parking brake follows the usual procedure, i.e. the first determined force value is used as the target value for keeping the vehicle stationary. Indeed, without the driver's supervision, the application force must be high to ensure the safety of the vehicle and prevent it from accidentally starting to move.

[0027] The braking method may further include one or more of the following optional features, taken alone or in combination:

[0028] – The parking conditions of the vehicle are at least the slope of the road on which the vehicle is located and the temperature of the friction means and / or the friction member.

[0029] – The slope is determined by a tilt sensor, called an inclinometer, or by an on-board computer in the vehicle.

[0030] – The slope value is an absolute value.

[0031] – The temperature is determined by estimation based on a braking command applied by the driver to the parking brake. Alternatively or in combination, the temperature is determined by means of a temperature sensor, advantageously located close to the wheels.

[0032] Thus the target clamping force value varies according to the slope and temperature conditions, in order to optimize the clamping force required to immobilize the vehicle, for example when it must be kept stationary on a zero or slight slope with a slight incline, for example an incline of less than 13%. In this case, the first clamping force value determined is low, for example around 10kN, and the second value is advantageously reduced compared to the first value. Energy consumption is therefore optimized by avoiding providing excessive clamping force and over-using the brake to immobilize the vehicle.

[0033] Similarly, for a low temperature, for example below 150°C, the target clamping force value is optimized.

[0034] – The difference between the second clamping force value and the first clamping force value is between X% and Y% of the first clamping force value, preferably at least Z%.

[0035] This results in a considerable reduction in the clamping force.

[0036] – The step of verifying the driver's presence at his driving position is carried out continuously.

[0037] This verification step is a safety step. It is carried out continuously to ensure that the driver is present to intervene if necessary, for example in the event of accidental release of the brake. This step is even more important for cars with an electric parking brake configured to activate braking when zero speed is detected. Indeed, the continuity of the verification step indirectly makes it possible to distinguish between parking and momentary braking, for example when the vehicle is held stationary at a traffic light. Depending on this distinction, the vehicle is held with a high safety brake application (first brake application value) or with a reduced brake application (second brake application value), the safety of which is ensured by the driver.

[0038] – The driver's presence at the driver's seat is checked based on a signal based on at least one of the following criteria: detection of the vehicle being switched on, detection of the driver's door being open or closed, visual detection of the driver, detection of the driver's seat belt being locked, detection of a mass on the driver's seat, detection of force exerted on the accelerator and / or brake pedal.

[0039] Detection based on these different criteria is carried out by means of different sensors integrated in the vehicle. The above list not only allows to verify the presence of the driver, but also to confirm an active and operational presence of the driver, i.e. that the driver is present in the vehicle during driving or in such a way as to be able to intervene in the braking process if necessary. For example, when the belt is unlocked, it could be deduced that the driver is not present or is going to get out of the vehicle and therefore that a high clamping force value would be required to immobilize the vehicle.

[0040] – The signal is for example the PbcInDriveAwayIntentionIndication signal, from the recommendation VDA305-100 v3 v2018 of the German Automotive Industry Association.

[0041] VDA305-100 is a generally known recommendation that explains the integration of brake controls into an electronic stability control (ESC), which is an active anti-skid safety device designed to improve vehicle trajectory control. The PbcInDriveAwayIntentionIndication signal is cited as an example; another type of signal that meets the requirements of the recommendations related to brake controls can be considered.

[0042] The invention also relates to a digital calculator comprising a memory and a processor connected to this memory, characterized in that said memory contains a series of instructions which, when executed by said processor, implement the method described above.

[0043] The invention also relates to a memory medium containing a series of instructions for implementing the method described above. Brief description of the figures

[0044] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0045] is a bottom view of a motor vehicle fitted with its brakes,

[0046] is a side view of the vehicle parked on a slope,

[0047] is a flowchart illustrating the algorithm executed by the digital computer to implement the method according to the invention. Detailed description

[0048] Figures 1 and 2 show a vehicle 1 parked on a slope 2. The vehicle is equipped with four wheels, two front wheels 5, 6 and two rear wheels 7, 8, mounted respectively on two axles 3 and 4. At least the two rear wheels 7 and 8 are equipped with parking brakes according to one embodiment of the invention. Each parking brake comprises an electric actuator 16 and friction means 14 acting on a disc 12 secured to the corresponding wheel.

[0049] A digital computer 20 is connected to the two electric actuators 16 to send them control signals intended to control the motor (not shown) of the friction means 14. A parking brake control member 18 is represented by a switch in the figure. This member is not necessarily a physical member. It can be constituted by a logic signal from an on-board computer. For example, the vehicle's on-board computer can be programmed to activate the parking brake when the driver switches off the engine and the vehicle speed is zero.

[0050] As is known, when a parking brake request is provided by the control member 18, the digital computer 20 detects this brake application request and retrieves the information reflecting the parking conditions of the vehicle, namely in particular the inclination of the road on which the vehicle is located, as seen in the. This inclination information can come from the vehicle's on-board computer or be measured by an inclinometer specifically provided for this purpose. From these parking conditions, the digital computer determines a first target application force value making it possible to keep said vehicle stationary for an unlimited period. The value thus determined can come from charts or tables pre-recorded in the computer.

[0051] For example, if the vehicle weighs 2500 kg and the slope on which it is parked has a 10% gradient (approximately 5.7 degrees from the horizontal), the first target value is 18.5 kN. With such a clamping force, even with a release over time due to the cooling of the friction means, the wheels would be locked.

[0052] According to the invention, instead of sending this first clamping force value as a setpoint to the actuators 16, the digital computer 20 carries out a check of the presence of a driver at the driving position of the vehicle. This check is not carried out directly by the digital computer 20. The driver presence information is provided by the on-board computer (not shown) or by specific sensors (not shown) provided for this purpose in the passenger compartment or on the pedals, levers, buttons and steering wheel likely to be manipulated by the driver.Various signals can indicate the presence of the driver in the vehicle's cockpit: detection of the vehicle being switched on, detection of the driver's door being open or closed, visual detection of the driver, detection of the driver's seat belt being locked, detection of a mass on the driver's seat, detection of force being exerted on the accelerator and / or brake pedal.

[0053] Thus, the digital computer executes the algorithm illustrated by the.

[0054] At step 21, the brake is released. No parking brake is requested.

[0055] In step 22, the computer tests the state of the control member 18. If the latter is positioned to signal a parking brake request, the process continues to the next step 23. Otherwise, it loops to step 21.

[0056] In step 23, the computer determines whether the driver is in the vehicle's cockpit. As already explained, this information is provided to the computer by external means. If so, the process continues with step 24. Otherwise, it continues with step 25.

[0057] Step 24: The driver's presence at the driver's seat is confirmed. The digital computer 20 reduces the first target tightening value by a predefined amount, to obtain a second target tightening value. It is this second target value that is sent as a setpoint value to the actuators 16.

[0058] Step 25: The driver's presence is not confirmed, the first target value is sent as the setpoint value.

[0059] The reduction applied to the first target value comes from a table of values, an example of which is provided in the following [table 1], where we see that not only the slope of the parking lot is taken into account, but also the temperature of the friction means.

[0060]

[0061] This reduction in the setpoint prevents excessive strain on the brakes and thus increases their service life. In addition, the energy required to operate the parking brake with a moderate application value reduces the amount of energy required for this operation. The energy saved has been estimated at more than 40% on average for a vehicle used under normal conditions.

[0062] For comparison, the following table shows the values ​​of clamping force, application time, release time and energy consumed in the case of the prior art and in the case of the invention. In particular, it can be seen that in addition to the reduction in energy consumed, the brake release time is shorter thanks to the invention, which improves the vehicle's responsiveness to driver input.

[0063] InventionState of the artTarget force value9500N14500NClamping force9769N14552NDuration of application0.87s0.99sRelease time0.82s1.04sEnergy consumed(application + release)33.05J57.01J

[0064] The invention is not limited to the embodiment presented and other embodiments will become apparent to those skilled in the art.

[0065] Reference list1: vehicle2: slope3: front axle4: rear axle5, 6: front wheels7, 8: rear wheels10: front brake disc12: rear brake disc14: friction means16: electric parking brake actuator18: parking brake control unit20: digital computer21-25: algorithm steps

Claims

Method for controlling a vehicle parking brake configured to apply a friction means (14) to a braking member (10, 12), comprising the following steps:- detecting (22) a request to apply the brake,- depending on the parking conditions of the vehicle (1), determining a target application force value making it possible to keep said vehicle stationary,- actuating the brake so as to provide an application force corresponding to the target value,characterized in that the step of determining a target application force value comprises the following steps:- determining a first application force value, making it possible to keep said vehicle stationary for an unlimited period, even after releasing the brake,- verifying (23) the presence of a driver at the driving position of the vehicle (1),- if the driver is present at his driving position, using (24) as the target application force value,of a second value strictly lower than the first clamping force value, - otherwise, use (25), as the target clamping force value, of the first clamping force value., Braking method according to the preceding claim, in which the parking conditions of the vehicle (1) are at least the slope (2) of the road on which the vehicle (1) is located and the temperature of the friction means (14) and / or of the friction member (10, 12). Brake method according to any one of the preceding claims, wherein the difference between the second clamping force value and the first clamping force value is between X% and Y% of the first clamping force value, preferably at least X1%. Braking method according to any one of the preceding claims, according to which the step of verifying (23) the presence of the driver at his driving position is carried out continuously. Braking method according to any one of the preceding claims, according to which the verification (25) of the presence of the driver at his driving position is carried out with regard to a signal based on at least one of the following criteria: detection of ignition of the vehicle (1), detection of an open or closed state of the driver's side door, visual detection of the driver, detection of locking of the driver's side seat belt, detection of a mass on the driver's side seat, detection of a force exerted on the accelerator and / or brake pedal. Brake method according to the preceding claim, wherein the signal is the signal PbcInDriveAwayIntentionIndication, of recommendation VDA305-100 v3 v2018 of the German Association of the Automotive Industry. Digital Computer (20) comprising a memory and a processor connected to this memory, characterized in that said memory contains a series of instructions which, when executed by said processor, implement the method according to any one of claims 1 to 6. Memory medium containing a sequence of instructions for implementing the method according to any one of claims 1 to 6.

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